NGC157
MCG 2-2-56
PGC 2081
Galaxy
Constellation: Cetus
RA: 00 34 46.6
DEC: -08 24 03
Type SAB(rs)bc
Mag: 10.4
Size: 4.2’ x 2.7’
Nearly 237 years ago to the date, William Herschel first observed NGC157 using his 18.7” speculum reflector on the 13th of December 1783. Positioned rather nicely between 2 ~8th magnitude stars just 4 degrees east of Iota Ceti. NGC 157 is a wonderful, nearly face on spiral in the constellation Cetus.
NGC 157 is unique in that its rotation curve, or the plotted orbital velocities of stars across its disk relative to the core, varies tremendously and actually increases the further one measures from the core ("1961ApJ...134..874B Page 874", 1961). A typical rotation curve one would expect to see shows velocities increase exponentially as you get closer to the core of a galaxy and drop off the further you are from the core. Not just that, this drop off, also called the “turnover point”, in gaseous and stellar velocities correspond with the drop off in luminosity of the galactic disk. NGC 157 actually exhibits a rise in orbital velocities, past this turnover point.
Back in 1959 when this phenomenon was first observed using the 82” at McDonald Observatory, astronomers were quite perplexed by these findings. Several theories have been brought forth to attempt and account for these measurements, including but not limited to (Kanipe & Webb, 2017.)
- A disturbance by a companion – even though one isn’t near enough to substantiate this claim.
- A dark matter halo.
- A merger of two equal mass gas disks some time ago
Whatever the reason, it makes for an interesting mental exercise while at the eyepiece to consider that something is effecting this galaxy in such a way that it doesn’t behave like your prototypical spiral galaxy.
Although I titled this weeks OOTW NGC157 The Superman Galaxy, I didn’t come up with the name. I’ve discovered that NGC 157 is also labeled as such on the ESO website. A few other individual observing reports I found online mention the moniker as well. But NGC157 isn’t alone as I feel several other objects are worthy contenders of the “Superman Galaxy” nickname. Our own Wouter makes mention of it in reference to Mark Friedmans OOTW on NGC7479 back in 2014. M83 – the first time I’ve heard of this - has been granted use of the nickname in this newspaper article from Naples Florida, although the author incorrectly refers to M83’s home constellation as Hydra, the sea monster. Even the incredibly stunning NGC 4535 The Lost Galaxy in Virgo could be deserving!
So in close, if you’re out observing this month, be sure to give NGC157 a go in the early evening. Visible in all manner of apertures, to best see the S in this “superman galaxy”, you’re going to want to use a bigger scope. The apparent S-shape, mottling throughout its arms as well as a nice bright concentrated core await you if you have access to a scope larger than about 18 inches. I have no record of ever seeing this object in Jimis 48 – I sure wish I did though.
As always,
“Give it a go and let us know! Goodluck and great viewing!”
HAWK-I.jpg
©HAWK-I ESO
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